DNA replication

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DNA replication
2010-12-13 17:50:45

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  1. Explain why DNA replication is important.
    • - everytime a cell divides, the 1st thing it has to do is copy it's genetic information
    • - division of cells in mitosis (growth and repair)
    • - before meiosis; before forming sex cells (reproduction)
  2. what does Helicase do?
    it attaches to DNA molecule, untwists and unzips it ( breaks hydrgen bonds) separating them completely
  3. what does Single Strand binding proteins do?
    latches on single protein strands, prevents them from coming together
  4. what does topoisomerase do?
    • -protein enzyme
    • - works ahead of replication fork
    • - prevents over winding of DNA strand
    • - takes DNA strand and cuts it, allowing it to unwind and rejoins it
    • - cuts s-phosphate backbone
  5. what does Primase do?
    • Adds RNA nucleotides to the 3' end of old strand
    • -anti parallel, the primer
  6. what does DNA polymerase do?
    latch onto primer
  7. define "leading strand of DNA"
    new strand and forms quicker
  8. define lagging strand of DNA
    formed slowly, and away from junction

  9. why are the leading and lagging strands forming in opposite directions?
    • b/c the DNA strand is anti-parallel,
    • - DNA polymerase can only add to the 3' end of DNA end

  10. explain how the synthesis of the leading strand and lagging strand of DNA are different.
    lagging strand: synthesis in sections, discontinuous replication, muliple primers, needs primer to be added and shifts, DNA polymerase has to let go and attaches
  11. Define okazaki fragments.
    short fragments of DNA that synthesis laggging strands of DNA in discontinuous fashion
  12. Explain how the okazaki fragments are joined to form a continuous lagging strand of DNA.
    get rid of primer, different DNA polymerase comes and removes primer, synthesize short fragments of DNA, gap is filled using DNA polymerase, then DNA ligase connects S-phophate backbone, seals the ends
  13. explain what is meant by "semi conservative DNA replication".
    we keep half of the DNA molecule and we used it as a platform to make a new complementary strand.
  14. 5" end of the leading stand and lagging strand contain RNA primers that once removed cannot be filled. Explain why.
    5' end never get replication b/c once primer is removed it cant latch on 5" end, cant work backwords so ends never get replaced
  15. what is the consequence of DNA strands getting shorter after replication process? why does this problem not exist in prokaryotes.?
    eat into genes, cant form essential proteins, cell is gonna due, thats why we age, our cells can only divide a certain amount of time.

    - prokaryotes have a circular DNA, no end, 2 ends are connected, the entire DNA is replicated
  16. define Telomeres.
    end segmentsa of DNA that code for nothing, repletitve and short
  17. explain why telomeres are important
    to protect the essential genes (down the line)
  18. explain why cancer cells can divide endlessly.
    outcomplete your normal body cells, normal cells deprive of oxygen, cancer cells take over and divides endlessly b/c they have an active telomerase
  19. How are ultraviolet radiation from the sun damages DNA?
    gets absorbed in pyrimidines, creates a bend which causes a covalent bond, which prevents DNA polymerase from progressing
  20. explain how DNA damaged by ultraviolet radiation from the sun is repaired.
    • 1. nuclease detects damage, makes cut on either side and removed danages piece
    • 2. DNA polymerase attached to 3' and starts complementary base pairing, fills the gap
    • 3. DNA ligase seals the ends of DNA
  21. what is Melanoma? cause? how it is detected? why it is so dangerous?
    • cells that produce dark pigment, skin cancer
    • CAUSE: excessive exposure to ultraviolet (UV) radiation from the sun
    • DETECTED: looking for a change in any mole or the appearance of new moles

    - errors in repair process of damaged DNA, gene that regulates cell division, end up with cancer cells